The invention relates to a projection objective with fixed focal length for digital projection, in particular for digital cinema. The projection objective finds application, for example, as the base objective with an anamorphic attachment.
Projectors used in digital cinema are characterized by a beam-splitter prism between the chips and the objective. The glass path length is up to 119.5 mm, whereby a longitudinal chromatic aberration and an aperture aberration arise.
Mainly, zoom objectives are offered on the market. However, for fixed installations, a zoom objective is not necessary. Moreover, the conversion of the chip format to the image format 2.35:1 advantageously takes place in digital cinema with the aid of an anamorphic attachment. In order to reduce the dimensions of the attachment and thus the costs, it is necessary that the screen side aperture diaphragm not be too far away from the front lens. This goal is difficult to achieve with zoom objectives.
Described in DE 103 53 563 B4 is a projection objective with fixed focal length for digital projection that displays nine lenses. This fulfills the above-mentioned requirements. However, in all of the specified embodiment forms, this objective contains an aspherical surface, which increases the production costs.
As will be appreciated by those skilled in the art, the present invention is directed to the physical consideration or aspects of the projection objective. Data concerning its structural design are not to be obtained from the present disclosure.
In order to realize an optimal reproduction quality with a projection objective, it is necessary to center the lenses most accurately in reference to the optical axis of the projection objective. Here an accuracy of centering of less than 1/1000 mm must be assured. Only then can an outstanding brilliance be achieved.